1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus that processes a sheet on which an image is formed (hereinafter referred to as a “printed sheet”) by a laser processing unit and, more specifically, relates to a sheet processing apparatus and an image forming apparatus that prevent collected scraps from being overheated by a laser beam.
2. Description of the Related Art
Some known image forming apparatuses, such as copy machines and printers, include sheet processing apparatuses that selectively carry out binding and punching on a printed sheet so as to reduce the trouble required for binding sheets after image formation.
There is a known sheet processing apparatus including a laser processing unit that is configured to cut a sheet in a desired shape by irradiating the sheet with a laser beam having a predetermined pulse (for example, refer to U.S. Pat. No. 5,797,320).
FIG. 16 illustrates the structure of a known sheet processing apparatus including the above-described laser processing unit. FIG. 16 illustrates a laser processing unit 7 including a laser generator 8, which generates a laser beam, and a lens 9.
The laser processing unit 7 focuses the laser beam generated at the laser generator 8 to a surface S of a sheet by the lens 9. In this way, power great enough to cut the sheet is obtained within a predetermined range of the laser beam (hereinafter referred to as a “processing range”) from a point that is a predetermined distance forward of the focal point to a point a that is a predetermined distance rearward of the focal point in the transmission direction of the laser beam. By controlling the laser beam in accordance with the desired shape, a product having the desired shape can be obtained.
With a sheet processing apparatus including the laser processing unit 7, when a printed sheet is discharged from an image forming apparatus main body (not shown), the printed sheet enters an inlet 16 and is conveyed along a conveying path 10 by a pair of first conveying rollers 12.
Then, the printed sheet is conveyed by a pair of second conveying rollers 13 and a pair of third conveying roller 14. At this time, the printed sheet passes below the laser processing unit 7 disposed above the conveying path 10. While the printed sheet passes below the laser processing unit 7, a laser beam cuts the printed sheet (hereinafter this cutting process is referred to as “laser cutting”). Finally, the printed sheet is discharged into a stack tray 15 by the third conveying roller 14.
As shown in FIGS. 16 and 17, a scrap box 11 opposes the laser processing unit 7 with the conveying path 10 interposed therebetween. By disposing the scrap box 11 at this position, scraps produced as a result of laser cutting can be collected without affecting the delivery of the sheet.
With such a known sheet processing apparatus and image forming apparatus, when the scrap box 11, which is a collecting portion, is disposed at a position opposing the laser processing unit 7, the amount of scraps Pd collected in the scrap box 11 increases as the cutting process is continued.
As the amount of stored (collected) scraps Pd of sheets increases, the upper surface of the scraps Pd moves closer to the processing range of a laser beam, where cutting by the laser beam is possible. When the scraps Pd of sheets approaches the processing range of a laser beam, the scraps Pd may be overheated by a laser beam generated when cutting subsequent sheets to be processed.